<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
<style>
    div{
        width: 100px;
        height: 100px;
        background: yellow;
        margin: 0 auto;
        box-shadow: 10px 10px 10px red inset;
        /*加了inset就变成内阴影*/
    }
</style>
</head>
<body>
    <div></div>
</body>
</html>